1. Field of the Invention
The present invention relates to novel aqueous colloidal dispersions of a compound of cerium (IV), supersaturated in OH.sup.- ions, and to a process for the production thereof.
2. Description of the Prior Art
It is known to this art, from Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Vol. 4, pg. 850, that it is possible to prepare a hydrated ceric dioxide corresponding to the formula CeO.sub.2.x H.sub.2 O, wherein x is a number ranging from 0.5 to 2, and in the form of a gelatinous precipitate, by the addition of sodium or ammonium hydroxide to solutions of ceric salts.
In French Patent No. 2,416,867 a process for the preparation of aqueous dispersions of cerium oxide is described, which process consists of formulating a suspension of cerium (IV) hydroxide with water and an acid capable of effecting the disintegration of the crystallites, and then heating the suspension for a period of time and at a temperature such that the pH attains a stable value, with the amount of the acid present in the suspension being such that said stable pH value is less than 5.4, and thereby producing a treated suspension into which water is incorporated to constitute an aqueous dispersion of cerium oxide.
It is noted in this '867 patent that the preparation of the hydrated cerium (IV) oxide may be carried out by the precipitation of a cerium salt. It is thus possible, for example, to dissolve a high purity cerous carbonate in a solution of nitric or hydrochloric acid, to obtain a neutral solution of cerous nitrate or chlorate, which is oxidized with NH.sub.4 OH/H.sub.2 O.sub.2 to provide hydrated cerium (IV) oxide.